Determination of factor of safety of a slope subjected to vibratory pile driving in 3D

Master thesis (2022)

Authors

A. Mohanty Civil Engineering & Geosciences

Contributors

C. Zwanenburg Geo-engineering - CEG (supervisor 1)
R.E.P. de Nijs Geo-engineering - CEG (supervisor 2)
A. Tsouvalas Dynamics of Structures - CEG (coach)
Faculty
Civil Engineering & Geosciences
Copyright: © 2022 Avinab Mohanty
Slope stability PLAXIS 3D Factor of safety
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Published Date

30-03-2022

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

Vibratory installation of piles and casings can be extremely economical, therefore the contractors prefer pile driving. When compared to impact pile driving, vibratory pile driving generates less noise but this installation method is still fraught with uncertainties (Rausche 2003). Environmental effects (such as ground vibrations) have negative impacts which could lead to damage and failure under special circumstances.

The vibrations from the pile driving generate excess pore pressures and cause settles leading to failure in slopes. As part of the optimisation of mooring places for inland shipping and small coasters in Calandkanaal, the port of Rotterdam authority had a number of mooring places modified in the second half of 2016. A point of attention was the lack of analysis and a testing framework as there were uncertainties in excess pore pressure generation, an exposed area in the slope and slope stability. Based on these uncertainties, the work presented in this report tries to bridge this gap by answering
the following research question:

How can the existing knowledge on pile driving by means of vibratory installation be efficiently integrated into a 3D model which can practically estimate the factor of safety of the slope during vibratory installations?

To answer the main research question, a few sub-questions were formed, which are as follows:

• How can the vibratory parameters be integrated to model the slope stability?
• What is the thickness of the highly degraded zone around the pile due to vibratory pile driving?
• What are the limitations of the study?

The proposed work uses the vibratory pile driving data to generate excess pore pressure data using an empirical pore pressure model given by Green & Mitchell (2004) referred here as the GMP pore pressure model. Along with the pore pressures by using an empirical attenuation relation, the extent of the liquefied zone was determined giving an idea about the area of the slope affected by pile driving.

For slope stability, PLAXIS 3D is used along with its flow module. PLAXIS 3D gives an idea of the expected displacements in the geometry (slope) and the factor of safety. In a way to incorporate vibration effects, only the pore pressure are used as load inputs because of the difficulty of inducing
pile driving vibrations in a static calculation.

To add pore pressures into the geometry, a well was used with the infiltration function for the amount of time the pile was driven in the actual project. The volume input for the well infiltration is calculated in the same way as it was done in the actual project shown in the work of de Nijs (2019). PLAXIS 2D and D-geo stability software packages are also used in an attempt to make comparisons with the PLAXIS 3D model and validate the whole analysis.